In a machine tool such as a grinder or a machining center, machining of a workpiece and cleaning of a jig are performed while a coolant is supplied to the workpiece in a machining section and the jig from a coolant tank. Chips of the machined workpiece and chips washed away from the jig are collected in the coolant tank together with the coolant, after large chips are collected by a chip conveyor. The collected coolant is filtrated by a filter disposed halfway in a piping route for supplying the coolant to the machining section and the like. Particulates mixed in the coolant are separated from the coolant and collected.
As the filter, a filtration type filter made of paper or cloth, such as a paper filter or a bag filter, is used. However, clogging easily occurs in the filtration type filter. Therefore, the filtration type filter needs to be periodically cleaned or replaced. Running costs increase and manpower is required for replacement work. In order to solve this problem, magnetic inline filters described in Patent Document 1 and Patent Document 2 are proposed.
In the magnetic inline filter of Patent Document 1, a double pipe is configured by a cylindrical sealed container and a treatment container on the outer side of the sealed container. A plurality of disc-like permanent magnets are stacked and disposed in a cylindrical space in the center of the sealed container. In an annular space between pipes of the double pipe, a number of small ferromagnetic filter members are filled. The filter members are magnetized by the permanent magnets. A coolant is caused to pass through gaps of the magnetized filter members and the filter members are caused to attract chips included in the coolant to separate the chips from the coolant. When the chips attracted by the filter members are accumulated and filtration efficiency falls, the permanent magnets are moved to a position completely off a position opposed to the filter members to demagnetize the filter members. The coolant is reversely fed to discharge the chips attracted by the filter members to the outside.
In the magnetic inline filter of Patent Document 1, since replacement filters are unnecessary, running costs can be reduced. However, since the disc-like permanent magnets are disposed only in the cylindrical space in the center, a magnetic field in a radiation direction is weak, magnetization of the filter members is weak, and there is a problem in filtration ability. In the magnetic inline filter of Patent Document 2, metal particles are filled in a plurality of circulation paths through which a coolant flows. The magnetic inline filter includes magnet housing sections along both the sides of the circulation paths. Permanent magnets are housed in the magnet housing sections. The permanent magnets are enabled to move between a filtration position for magnetizing the metal particles and a cleaning position for separating the permanent magnets from the metal particles to release the metal particles from magnetism.
Also in the magnetic inline filter of Patent Document 2, replacement filters are unnecessary. Therefore, it is possible to reduce running costs. However, since the plurality of circulation paths and the plurality of magnet housing sections are formed narrow and slender, structure is complicated and it is difficult to dispose a number of permanent magnets to intensify a magnetic field.